1. MAPH40410 Synoptic Meteorology Meteorology M.Sc. Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin

2. MAPH40410 Synoptic Meteorology Synoptic Meteorology MAPH 40410 Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin

3. MAPH40410 Synoptic Meteorology Forecasting Module Lecture 1 Refresher: Airmasses, Fronts & Frontal Depressions

4. MAPH40410 Synoptic Meteorology Polar Maritime Returning Polar Maritime Tropical Maritime Tropical Continental Polar Continental Arctic Maritime Air Masses

5. MAPH40410 Synoptic Meteorology Norwegian Model

6. MAPH40410 Synoptic Meteorology 167 181 64 045 10 1/30 Mean sea level pressure Last 3 figures of the MSL Pressure e.g... 181 = 1018.1hPa Present weather Symbols Rain Drizzle Snow Showers Thunderstorm Fog Phenomena occurred in past hour. Visibility 01 to 50 add 00 for visibility in metres 56 to 89 subtract 50 for visibility in km Cloud amount and height ( Low, Medium and High) Amount of cloud in eighths /height of cloud in feet 01 to 50 add 00 for height in feet 56 to 89 subtract 50 for height in thousands of feet Past weather Symbols as Present weather Period covered 0000,0600,1200,1800 last 6hrs 0300,0900,1500,2100 last 3hrs All other hours last hour Type of low cloud Dew point in tenths of a degree e.g.... 045 = 4.5 C Screen temperature in tenths of a degree e.g... 167 = 16.7 C Type of medium and high cloud. Decode over page Change in pressure (tendency) Difference in pressure from 3 hours in tenths of hPa and direction of up or down. Decode over page Windspeed and direction Wind from direction of the shaft Triangle = 50 kts Full feather =10 kts Half feather = 5 kts Just shaft < 3kts The Station Circle

7. MAPH40410 Synoptic Meteorology Observations 012 65 9 7 24 11, 45 10 50 35 001 997 11 30 15 997 8 4 75 007 06 20,, 9

8. MAPH40410 Synoptic Meteorology Tephigrams & Stability Any point on an ascent Absolutely Unstable Absolutely Stable Conditionally Unstable The position of the ELR gives the stability of the ascent at that point DALR > SALR > ELR ELR > DALR > SALR DALR > ELR > SALR

9. MAPH40410 Synoptic Meteorology EXTRATROPICAL CYCLONES   They form along the line between the polar air mass and the maritime tropical air mass.   Shearing produces cyclonic motion.   Under suitable conditions frontal surface will assume a wave shape.

10. MAPH40410 Synoptic Meteorology EVOLUTION OF A FRONTAL DISTURBANCE initial stage open wave cyclone occludingfully occluded (mature) stationary polar front

11. MAPH40410 Synoptic Meteorology INITIAL DISTURBANCE

12. MAPH40410 Synoptic Meteorology OPEN WAVE DEPRESSION

13. MAPH40410 Synoptic Meteorology OCCLUSION BEGINNING

14. MAPH40410 Synoptic Meteorology FULLY OCCLUDED

15. MAPH40410 Synoptic Meteorology LIFE-CYCLE OF A AN EXTRATROPICAL CYCLONE

16. MAPH40410 Synoptic Meteorology 1 3 24 Lifecycle of frontal disturbances Surface isobars (solid) temperature (dashed)

17. MAPH40410 Synoptic Meteorology 2 1 3 4 Upper-level Height Contours Note displacement of upper-level trough to west of surface low

18. MAPH40410 Synoptic Meteorology RELATIONSHIP BETWEEN SURFACE CYCLONE AND UPPER LEVEL FLOW 500 mb height (thick lines), SLP isobars (thin lines), and layer-mean temperature (dashed). The deflection of the upper-level wave contributes to deepening of the surface low.

19. MAPH40410 Synoptic Meteorology CYCLOGENESIS   Formation of cyclones   Close relationship between surface disturbances and flow of air aloft.   For a mid-latitude cyclone to form: cyclonic flow must be established   Inward flow of air near surface must be supported by outflow aloft.   Total spin / cyclonic height = constant

20. MAPH40410 Synoptic Meteorology The jet stream wind is subgeostrophic in troughs, and supergeostrophic in ridges slow fast slow

21. MAPH40410 Synoptic Meteorology slow fast

22. MAPH40410 Synoptic Meteorology slow fast

23. MAPH40410 Synoptic Meteorology

24. Mid-latitude Frontal Disturbances: interaction between low-level and jet-level flow SL pressure and precipitation300 mb height and wind speed cold warm

25. MAPH40410 Synoptic Meteorology surface low upper-level trough Developing frontal lows tilt westward with height

26. MAPH40410 Synoptic Meteorology slow fast Note the advection of cold and warm airmasses

27. MAPH40410 Synoptic Meteorology Satellite Views of Wave Cyclones Open stage, with clouds over warm and cold fronts, with clear warm sector Occluding stage Mature stage

28. MAPH40410 Synoptic Meteorology mature stage occluding stage

29. MAPH40410 Synoptic Meteorology Locate the fronts and surface low

30. MAPH40410 Synoptic Meteorology

31. IR image

32. MAPH40410 Synoptic Meteorology Water vapour image

33. Finding Surface Fronts Using plotted surface charts

34. MAPH40410 Synoptic Meteorology Finding Surface Fronts   What is a front?   A boundary between different types of air   If we can define what those differences typically are, or what we expect them to be …   … we can define the things that we should look for in order to find a front

35. MAPH40410 Synoptic MeteorologyFronts warm aircold aircool air

36. MAPH40410 Synoptic Meteorology ASXX MSLP Analysis 1200 UTC 20 Apr 2000

37. MAPH40410 Synoptic Meteorology Fronts on a Pressure Chart 992 988 984 980 976 972 996 1 2 3 4

38. MAPH40410 Synoptic Meteorology Station Circles   By studying different elements on a station circle, the position of the surface front can be found   So, what’s available on a station circle?   temperature and dew point   wind speed and direction, gusts   present and past weather, visibility, cloud amount, cloud type, cloud base   pressure tendency

39. What happens to the weather as a front passes? Using the information from station circles

40. MAPH40410 Synoptic Meteorology Fronts on a Pressure Chart 992 988 984 980 976 972 996 1 2 3 4

41. MAPH40410 Synoptic Meteorology >200km ahead of the warm front 12 07 965 07 251 75 4 1

42. MAPH40410 Synoptic Meteorology In the warm sector, 20km ahead of the cold front G32 11 09 752 31 188 608 50 2

43. MAPH40410 Synoptic Meteorology 20km behind the cold front 08 06 814 18 257 112 65 3

44. MAPH40410 Synoptic Meteorology >100km behind the cold front 08 04 840 12 328 72 4

45. MAPH40410 Synoptic Meteorology Positioning a Surface Front   Temperature and Dewpoint   Windspeed and Direction, Gusts   Present Weather and Past Weather   Visibility   Cloud Amount, Type and Lowest Cloud Base   Pressure Tendency

46. MAPH40410 Synoptic Meteorology Temperature and Dewpoint   Temperature isn’t such a good guide as dewpoint   The dewpoint within an airmass tends to remain the same   The dewpoint in the warm sector will be constant and fairly high   The dewpoint behind the cold front may fall gradually

47. MAPH40410 Synoptic Meteorology Wind speed and direction   The wind will veer on the passage of a front   Veer = turn clockwise   Back = turn anticlockwise   Gusts are likely to be strongest on the cold front

48. MAPH40410 Synoptic Meteorology Present and Past Weather The heaviest rain is often at the front   It is likely to rain ahead of a warm front   Drizzle is most likely in the warm sector   Showers develop behind a cold front

49. MAPH40410 Synoptic Meteorology Visibility   Visibility decreases when it is raining   Drizzle will decrease the visibility more than rain (the smaller drop size is more effective at scattering light)   Visibility in the warm sector will generally be poorer   Visibility in the cold air will be very good, up to 30km or more

50. MAPH40410 Synoptic Meteorology Clouds   Amount and type   High clouds >200km ahead of the warm front   Lowest cloud is associated with the heaviest rain, often on the front   Cloud base can be affected by orography

51. MAPH40410 Synoptic Meteorology Pressure Tendency   The pressure falls just ahead of a front and rises just behind it, giving a pressure ‘kick’ Pressure

52. MAPH40410 Synoptic Meteorology Positioning a Surface Front   Dewpoint - constant in the warm sector   Winds veer as a front passes   Drizzle in the warm sector   Moderate or heavy rain on the cold front   Showers behind the cold front   Overcast in the warm sector   Broken cumulus behind the cold front   Pressure ‘kick’ as a front passes

53. MAPH40410 Synoptic Meteorology Conclusion. Questions welcome